1. Field of the Invention
The present invention relates to a navigation system that provides a driver with route guidance information by displaying the maps and intersections surrounding the driver""s vehicle.
2. Related Art
In general, a navigation system for a vehicle detects the current position of the vehicle and reads out the map data for the area surrounding the vehicle from a storage medium such as a CD, DVD, and the like to present the map on a display. The system also displays a vehicle position mark that illustrates the vehicle position at a specific place on the display, and scrolls the map surrounding the vehicle to follow its movement with the vehicle position mark in the center, whereby the driver is kept informed of the map information for the area surrounding the vehicle position.
Further, almost all of the recent vehicle navigation systems are equipped with a route guidance function whereby a user is able to travel to a desired destination without taking a wrong road. This route guidance function automatically searches for the route of a minimum cost that connects the starting point and the destination set by the user, and draws the searched guidance route thicker on the map with a different color than the other roads. When the vehicle approaches an intersection on the guidance route, the system also displays an enlarged map for the area surrounding the intersection, and displays an arrow, for example, indicating the lane that the vehicle should take, whereby the user is able to recognize the route to take.
When guiding along the travel lanes in the intersection (hereunder, referred to as xe2x80x9cthe first intersectionxe2x80x9d) that the vehicle is about to pass through, the conventional navigation system does not pay attention to the state of the guidance route after passing through the first intersection, and displays an arrow or the like to all the lanes that the vehicle can take when passing through the first intersection. However, there is a possibility, depending on the state of the guidance route, that all the lanes that the vehicle can take at the time of passing through the first intersection are not always appropriate for the travel along the guidance route thereafter.
As a specific example, suppose that the vehicle travels straight through the first intersection along the guidance route, and turns right at the next intersection (hereunder, referred to as xe2x80x9cthe second intersectionxe2x80x9d). It is also assumed that there are three lanes at the first intersection, all of which are directly advancing lanes, and there are three lanes at the second intersection, among which two are directly advancing lanes and one is a right-turn lane. In such a situation, considering that the vehicle turns right at the second intersection, it is desirable that the vehicle should change the travel lane into the right lane at the first intersection if possible. However, in the guidance of the travel lane in the conventional navigation system, when the vehicle travels in the left lane of the three directly advancing lanes immediately before passing through the first intersection, the system will display arrows or the like on all three lanes as a lane that the vehicle can take, since the three lanes are directly advancing and the guidance route at that moment is directly advancing at the first intersection. The driver, viewing this guidance of the travel lane, might remain in the left lane that the vehicle took until then.
Here, if the distance between the first intersection and the second is relatively short, or if there is much traffic on the road, the driver will not be able to change the travel lane into the innermost right-turn lane before the vehicle reaches the second intersection, after the lane guidance relating to the second intersection is presented. Consequently, the vehicle travels along a lane that deviates from the guidance route at the second intersection.
As described in the foregoing example, lane guidance at an intersection that the conventional navigation system provides has the problem that it does not provide a more appropriate travel state in consideration of the state of the guidance route after passing through the first intersection.
The present invention has been made in view of the foregoing problem, and it is an object of the invention to provide a navigation system whereby a vehicle can receive the appropriate travel state as described above. In order to accomplish this, in the navigation system of the invention, a route search means executes route search processing to thereby set a travel route of a vehicle. On the basis of the set travel route, a guidance information setting means sets guidance information concerning a first intersection that the vehicle passes, in consideration of the conditions of passage at a second intersection that the vehicle passes thereafter, and an intersection guidance means communicates the set guidance information to the driver. Thereby, since the navigation system is able to provide guidance concerning the first intersection that the vehicle is going to pass, in consideration of the conditions of passage at the second intersection that the vehicle passes thereafter, the driver easily attains an appropriate travel state.
Further, it is preferable that the guidance information set by the guidance information setting means includes information concerning the recommended travel lanes when the vehicle passes the first intersection, and the intersection guidance means communicates the guidance information by distinctly displaying the recommended travel lanes. Consequently, since the navigation system provides guidance of the travel lane suitable for passing the second intersection after passing the first intersection, the driver is able to avoid an abrupt lane change or a useless lane change after passing the first intersection, and to attain an appropriate travel state with fewer lane changes.
It is also preferable that, when the second intersection is an intersection where the vehicle makes a right-turn or a left-turn next, the guidance information setting means sets guidance information that minimizes the lane change frequency until the vehicle reaches the second intersection. When there are lanes having the same travel conditions, for example, when there are plural directly advancing lanes at an intersection where the travel route of a vehicle is set as directly advancing, since the vehicle is able to travel with the minimum lane change frequency, the driver easily attains an appropriate travel state.